a) Field of the Invention
The present invention relates to enzymatic deinking of waste paper and a deinking composition.
b) Brief Description of Prior Art
Deinking represents primarily the process of extracting ink and toner from secondary fibre.
The traditional basic steps in conventional de-inking, that can be arranged in many different configurations, are described in part in TAPPI Journal pp. 101-106; D. R. Crow and R. F. Secor “The Ten Steps of Deinking ” Jul. 1987. These steps are:    1) PULPING, usually done by batch and sometimes continuously. In this stage wastepaper and water are pulped for about 60 minutes, at about 55-70° C., at consistencies between 8-16% in the pulper. Stock consistency is subsequently dropped to around 4-5% before reaching the dump chest. Chemicals used mostly in the pulper stage and sometimes in some of the following stages are described in Pulp & Paper pp. 59-63;            T. W. Woodward” Appropriate Chemical Additives Are Key to Improved Deinking Operations” Nov., 1986. These chemicals are:        a) Sodium hydroxide at 3.0-5.0% on the fibre, for ink break-up through fibre swelling, for ink vehicle saponification and/or hydrolization and for ink dispersion.        b) Sodium silicates for wetting, peptization, ink dispersion and emulsification, alkalinity and buffering, peroxide stabilisation and preventing hydrolysis of soaps, at 2.0-6.0% on the fibre.        c) Hydrogen peroxide for oxidative bleaching and fibre yellowing prevention.        d) Fatty acids (e.g. stearic acid) at 0.5-3.0% on the fibre, as ink flotation aids.        e) Surfactants (e.g. ethoxylated linear alcohols or ethoxylated alkyl phenols) at 0.2-2.00% on the fibre, for ink removal, ink dispersion, wetting, emulsification, solubilization.        f) Sodium or potassium phosphates at 0.2-1.0% on the fibre as metal ion sequestrants, and for ink dispersion, alkalinity, buffering, detergency and peptization.        g) Sodium carbonate at 2.0-5.0% on the fibre for alkalinity, buffering and water softening.        h) Solvents (e.g. C1-C14 aliphatic saturated hydrocarbons) at 0.5-2.0% on the fibre for ink softening and salvation.        i) Hydrophilic polymers e.g. polyacrylates at 0.1-0.5% on the fibre, for ink dispersion and ink anti-redeposition or modified polyester resins as ink flotation aids.            2) PREWASHING, made by a de-watering screw that increases stock consistency from 4-5% (dump chest) to 14-16%. The effluent from this step is re-circulated to a chest used for pulper makeup. This effluent can be treated by additional devices such as:            a) Sidehill-type screens for fine removal;        b) Flotation cell for removing a large portion of ink and clay;        c) Clarifier for fines, ink, and clay removal; and        d) Settling tank for clay removal.            3) SCREENING, done by:            a) Coarse screens—The stock is pumped through a centrifugal cleaner to a pressure screen with 1.5-2 mm diam holes. Rejects are deflaked and passed through a vibrating screen with 3-5 mm. diam. holes.        b) Fine screens—The stock is pumped through medium density cleaners to remove staples, paper clips and other larger, heavier contaminants, to pressure screens with fine slots (0.25-0.35 mm). This system often has three to four stages. This screening system is the most effective against stickies.            4) THROUGH CLEANING (REVERSE CLEANING), made with through-flow cleaners and reverse cleaners with low-pressure drops (10-15 psi) and low hydraulic rejects (5-15%). Conventional systems consist of two to three stages. They are effective in removing stickies, plastics, styrofoam wax.    5) FORWARD CLEANING, having the purpose of removing contaminants too small for the fine slotted screens with a density that allows them to be accepted by medium density cleaners and through-flow cleaners (or reverse cleaners). These cleaners operate best at low stock consistency (e.g. 0.6%) and they are typically organized in three stages.    6) WASHING, done with the main purpose of removing small ink particles (less than about 50 microns). It is performed by washers of the following types:            a) De-watering screws;        b) Gravity deckers;        c) Sidehill screens;        d) Single wire devices;            7) FLOTATION, having the main purpose of removing bigger ink particles from pulp (up to about 200 microns). In this step, ink attaches preferentially (in relation to fibre) to air bubbles through a mechanism based on its hydrophobicity. The ink containing foam is subsequently removed to rejects.    8) DISPERSION targeting ink dispersion for size reduction and for release from fibre surface. Is effective for difficult to remove inks: ultraviolet inks, xerographic inks, jet-print inks. The mechanical action at medium consistencies (10-14%) or high consistencies (25-35%) is performed under temperature conditions of 120-190° F. This stage often has a chemical component. Dispersants can be very effective in reducing ink particles size and therefore help in a subsequent washing step.    9) BLEACHING done often in the pulper. Other bleaching points are after the heat and mechanical de-watering screw and/or after the last washer or flotation cell. Besides hydrogen peroxide already mentioned, some of the other common bleaching agents are sodium hydrosulfite, FAS (formamidine sulfinic acid) and sodium hypochlorite.    10) WATER RECIRCULATION, MAKEUP AND WASTE HANDLING representing the final step. Water recirculation is possible through clarifiers that remove ink, fillers fines and stickies, usually by DAF (dissolved air flotation) and using retention polymers. Makeup water originates from clarifiers and from outside sources: paper machine white water and fresh water. Bleeding a minimum flow from the system is essential for controlling dissolved solids. Solid waste represents another important issue.
During the last fifteen years several synergistic evolutionary developments modified the conventional approach to deinking, as mentioned in part in PaperAge; K. Patrick” Advances in Paper Recycling Technologies” Jul. 2001, O'Brien Publications, Inc.
These recent advances are:
1) IN PULPING. High consistency pulpers allow better ink detachment, lower pulping                time and better ink particle dispersion. They allow, together with improved de-inking chemicals:        a) Pulping with simplified chemical treatment (e.g. sodium hydroxide and surfactant                    or surfactant and silicate only),                        b) Extremely low dosages for the chemicals still used (e.g. surfactants at 0.01% on                    the fibre, while the traditional level was 0.20-2.00%)                        c) Only surfactant based chemistry,        e) No deinking chemistry at all,        f) Lowering pulping temperature at around 35° C.,        g) Reducing pulping time at about 15-25 minutes        Also, drum pulpers (continuous batch system) became predominant in newly built mills due to a gentler mechanical action that allows ink particles to remain initially larger and therefore generate an increased efficiency for the initial screening step. This improves subsequently the entire deinking process.        Treating pulp with enzymes that dislodge and remove ink in the pulper or later in the process, was shown in CA2032256 (Korea Research Institute of Chemical Technology) to reduce the use and unwanted effects of traditional chemicals. Similar results were obtained with starch degrading enzymes as described in U.S. Pat. No. 5,879,509 (Novonordisk AS).            2) PREWASHING. The importance of this step diminishes in the context of the overall de-inking technology improvements.    3) SCREENING. The major evolution in this deinking step was the reduction of fine screens from 0.25-0.35 mm to slots as small as 0,1 mm. This improved contaminant removal and overall efficiency of the system.    4) REVERSE CLEANING. A better screening and forward cleaning impacts on the use of reverse cleaners. Many plants, excepting OCC (old corrugated cardboard) plants, are shutting them down.    5) FORWARD CLEANING. Today's centrifugal cleaners used early in the system are typically smaller in diameter and are designed to remove bigger sized contaminants while operating at higher consistencies. Later in the process cleaners become even smaller.    6) WASHING. This step is losing some of its importance because of flotation improvements and because of high level of fine loss in traditional de-inking. New vacuum washers in ONP are retaining more fillers and fines.    7) FLOTATION. The latest flotation cells are completely redesigned (e.g. novel air injection nozzles that significantly improve bubble size distribution) and provide ink removal efficiencies unsurpassed historically.    8) DISPERSION. OCC and SOW (sorted office waste) plants are still relying on mechanical dispersion through dispergers or kneaders. As in pulping, or flotation, better surfactants brought lower chemical dosages for better ink-size particle reduction and ink removal.    9) BLEACHING. Today the most efficient bleaching for de-inked pulps seems to involve a pressurised oxygen-peroxide stage. Sodium hypochlorite is used less and less for environmental reasons, while a reduced number of plants are using chlorine dioxide. Ozone is rarely used. Hydrogen peroxide, sodium hydrosulfite and FAS are still widely used.    10) WATER RECIRCULATION, MAKEUP WATER AND WASTE HANDLING.            Improved control over clarifiers and retention polymer addition and performance are helping maintaining cleaner systems. Other ways to compensate for the increase in the volume of stickies entering the systems experienced in the last years are modern screening, cleaning, washing, flotation, mechanical dispersing and chemical solutions. These chemical solutions are:        a) Pacification: rendering stickies less tacky (e.g. with talc, clay);        b) Dispersion: reducing particle size (with dispersants);        c) Solvating: dissolving particles (with solvants);        d) Fixation: attaching stickies to the fibre (with cationic water soluble polymers).        A novel technology described by CA2412757 (Buckman Laboratories) that uses enzymes (lipases and/or esterases) also controls contaminants.        Enzymes are in this case mainly process chemicals having the purpose of reducing production problems related to contaminant deposits on machine surfaces, fabrics, wires, felts, and rolls.        
The accelerated evolution of deinking in the last two decades shows clearly the need for any mechanical and/or chemical solutions that can improve any aspect of this process. This is due to a constant need to lower production cost with an increased product quality in the context of more and more closed mill effluent systems and increasing environmental concerns. However, one of the most important objectives of deinking remains extracting ink/toner from secondary fibre and a final pulp with the highest brightness and lowest visible remaining dirt possible remains a major priority for any de-inking mill. While today deinked pulp can be a cost-effective component in newsprint and tissue, it still has limited use (typically only 10-30% from the entire volume of pulp used) in grades of fine paper like printing and writing grades. In these grades the presence of small visible specks of ink are usually considered unacceptable.
Currently, enzymes are used for dislodging and removing ink particles from wastepaper, as described in CA 2032256 (Korea Research Institute of Chemical Technology) or by starch degrading action as described in U.S. Pat. No. 5,879,509 (Novonordisk AS).
The current enzymatic deinking is targeting one or some of the substrates involved in ink retention in the final pulp. Examples of these substrates are: cellulose, pectin, hemicellulose—especially xylan, amylose, amylopectin, and other carbohydrates. All these substrates are located mostly on the surface and in the internal waste paper structure and/or on the interface between paper and ink formed by starch containing coatings or size-press applied layers. Some of these substrates originate from the wood structure, including cellulose, pectin, hemicellulose—especially xylan, and other carbohydrates. Others, including amylose, and amylopectin were mainly added during paper or cardboard production, internally for dry strength and/or externally, usually as low cost binders in surface treatments.
The present invention improves current deinking with enzymes by improving results obtained through dislodging and removing ink particles and/or through starch degrading with a third general deinking mechanism: namely an ink/toner dispersing action.